Polyethylene terephthalate

ABSTRACT

1. A COMPOSITION COMPRISING: (A) POLYETHYLENE TEREPHTHALATE (B) FROM 0.5 TO 10 WEIGHT PERCENT OF FINELY PARTICULATE RED PHOSPHORUS (C) FROM 2.0 TO 5.0 WEIGHT PERCENT OF A METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF MGO, TIO2, ZNO, MOO3, AL2O3, ZR2O3, CR2O3, WO2O3, B2O3, MNO2, CDO, SNO, PB2O3, BI2O3, SB2O5.

United States Patent 6 3,847,861 POLYETHYLENE TEREPHTHALATE TheodoreLargman, Morristown, and Herman Stone, Convent Station, N.J., assignorsto Allied Chemical Corporation, New York, N.Y.

No Drawing. Continuation of abandoned application Ser. No. 180,516,Sept. 14, 1971. This application Mar. 12, 1973, Ser. No. 340,636

Int. Cl. C08g 51/04 US. Cl. 260--40 R 12 Claims ABSTRACT OF THEDISCLOSURE Incorporated of finely particulate red phosphorous intounfilled or glass-filled polyethylene terephthalate provides a polymerhaving superior physical properties and flame retardance. Certain metaloxides exhibit a potentiating effect with the red phosphorous in regardto flame retardance.

This is a continuation of aplication Ser. No. 180,516, filed Sept. 14,1971, now abandoned.

BACKGROUND OF THE INVENTION Glass fiber-filled polyethyleneterephthalate is a Widely used structural and component plasticpossessing numerous desirable characteristics. The glass fiber enhancesthe physical properties of the polyethylene terephthalate. Inparticular, Izod impact strength, initial modulus of elasticity, andultimate tensile strength are all improved by the incorporation of to 40weight percent glass fiber into polyethylene terephthalate, hereinafterP-ET. However, the incorporation of glass fiber unfortunately has anadverse effect on the flammability of PET in comparison withnon-glass-filled PET. In view of the increasing emphasis on providingflame resistant polymers in all possible applications, it wouldobviously be highly desirable to provide a glass-filled PET whichnonetheless possessed fire retardancy superior to ordinary glass-filledPET. Needless to say, if such enhanced fire retardancy could be providedwhile simultaneously improving still further the physical properties ofthe glass-filled PET, a truly remarkable advancement in the state of thepolymer art would be provided. Also, in many instances, it is desirableto provide a non-glass-filled PET which has superior fire retardance andphysical properties in comparison with conventional unfilled PET.

SUMMARY OF THE INVENTION This invention therefore relates to fireretardant PET and more particularly, to both unfilled and glass-filledPET having improved physical properties and flame retardance whereinsaid improvements are imparted by incorporating into said unfilled orglass-filled PET a finely particulate red phosphorous.

It has now been found in accordance with the instant invention that PETcontaining 5 to 40 weight percent glass fiber and having homogeneouslydispersed therethrough from about 0.5 to about 10.0 weight percent,based on the weight of the glass-filled PET, of a finely particulate redphosphorous displays superior physical properties and flame retardancyin comparison with non-phosphorouscontaining glass-filled PET. The termfinely particulate, as used herein, connotes a particle size of lessthan 100 1. (microns), and preferably less than 25 1..

It has further been found in accordance with the instant invention thatwhen about 2 to about 5 weight percent of certain metal oxides areincorporated into the glass-filled PET along with the red phosphorous,several unexpected and unusual beneficial results are achieved.

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First, although these oxides by themselves have no discernible fireretardant effect when incorporated in these amounts into glass-filledPET, when present in conjunction with red phosphorous, the fireretardant effectiveness of the latter is substantially enhanced. Thesemetal oxides are therefore not true synergists but rather potentiatingor enhancing agents. Alternatively, the same degree of fire retardancecan be imparted to the PET by using metal oxide and less red phosphorousas can be achieved by a substantially greater quantity of redphosphorous alone. In general, it is desirable to use as little redphosphorous as will achieve the desired degree of physical property andfire retardancy improvement. The reason for this will be apparent whenone considers the manner in which the red phosphorous is incorporatedinto the PET.

Ordinarily, PET in the form of powder or pellets and the desired amountof finely divided red phosphorous, metal oxide, and fiber glass, *Wheredesired, are mixed together and agitated in a low-intensity mixer toachieve a reasonably uniform semi-homogeneous mixture and thissemi-homogeneous mixture then extruded to afford a glass-filled PEThaving the red phosphorous, metal oxide, and glass fiber uniformlydistributed therethrough. As heretofore indicated, after homogeneousincorporation into the PET, the red phosphorous serves as an eifectivefire retardant. However, prior to such homogeneous incorporation, and inparticular in the extruder chamber, any red phosphorous not actuallyalready incorporated into the PET may ignite due to the high temperatureconditions present (ordinarily from about 260 to about 300 0).Therefore, the less red phosphorous which needs to be blended with thePET to achieve the desired degree of physical property and fireretardancy, the better from a saftey standpoint.

An alternate method of incorporating the red phosphorous, metal oxide,and fiber glass is to add all three with agitation to molten PET, whichmolten mixture is then extruded. Here again, because of the hightemperatures involved, it is desirable for safety reasons to use aslittle red phosphorous as possible.

Finally, it is possible to prepare pelletized PET containing glass fiberand/or metal oxide and then admix these pellets with the red phosphorousand thereafter extrude. This method does not show any significantprocessing safety advantage over the above processes wherein metaloxide, red phosphorous, and glass fiber are simultaneously blended withthe PET.

We have found the following metal oxides to be most effective aspotentiating, i.e., enhancing, agents for red phosphorous: MgO, TiO ZnO,M00 and A1 0 and particularly MgO. The following metal oxides are lesseffective although they do, to a more limited extend, enhance theeffectiveness of red phosphorous: Zr O Cr O WO203, B203, M1102, S110,PbzOg, Bl20 and Sb O' The appropriate particle size range for the metaloxides is in general the same as for the red phosphorous, i.e. less than100,11. and preferably less than 25 If desired, mixtures of any or allof the above-indicated metal oxides can be used. If desired, othercompounds known to possess activity as fire retardants when incorporatedinto- PET can also be added, such as hexabromobenzene or zinc borate.Dark coloring agents or other conventional additives can also beincorporated.

When a combination of red phosphorous and one of the preferred metaloxides is added to glass-filled PET, the preferred concentration of eachis independently about 2.4 to 5.0 weight percent based on the weight ofglassfilled PET. Greater than 5.0 weight percent metal oxides has asignificant deleterious effect on the physical properties of the PET,although greater than 5.0 weight percent metal oxide continues toenhance the fire retardant properties of the red phosphorous. Less thanabout 2.0 Weight percent metal oxide shows only a marginal fireretardant enhancement effect.

Among the physical properties of glass-filled PET which we have foundare improved by the incorporation therein of red phosphorous incomparison with glass-filled PET not containing red phosphorous areultimate tensile strength, Izod impact strength, initial modulus ofelasticity, and ultimate elongation. These properties shall be discussedin more detail hereinafter.

The flammability of polymers is generally evaluated by several testsincluding the Fenimore-Martin Oxygen Index Test and the UnderwritersLaboratories Vertical Burn Test, UL 94. These tests are more fullydescribed hereinafter. For present purposes of discussion, it need onlybe noted that glass-filled PET gives unacceptable results in both tests.The plastics industry has therefore expended substantial time andexpense in an effort to provide a flame-retardant glass-filled PET whichachieves an acceptable level of flame retardance without adverse effecton the physical, chemical or processing properties in comparison withordinary glass-filled PET. Such efforts have heretofore not beencompletely successful.

Just why red phosphorous, which is soft, amorphous, and essentiallyinsoluble in the PET, has an enhancing effect on the glass-filled PETphysical properties is not known. Likewise, the reason for thepotentiating effect of the metal oxide on the fire retardant effect ofthe red phosphorous is not known to the inventors. Indeed, although redphosphorous has been reported to have a flame retardant effect whenincorporated into other polymer systems such as styrene/acrylonitrileand epoxy polymers, even in such cases, the reason for this lattereffect is apparently unknown.

As is well known, the term PET connotes the polyester derived fromterephthalic acid and ethylene glycol. The PET used in the instantinvention may suitably have a number average molecular weight of 10,000to 80,000 corresponding to an intrinsic viscosity ranging from about 0.3to about 1.5 as determined in 60/40 phenol/tetrachloroethane at 25 C.Higher and lower molecular weight PET can, of course, be used but is notgenerally available.

The glass fibers incorporated into PET ordinarily have a length rangingfrom about 0.1 to mm. and a diameter of 0.0005 to 0.025 mm. Glass fibersoutside these lengths and diameter ranges can be used but are notgenerally commercially available and provide no significant advantage.

The red phosphorous containing, glass-filled PET of the instantinvention can be formed into moulded articles, e.g. electricalconnectors or structural parts for telephones, computers, and TV sets,small power tool housings, and the like, by conventional mouldingtechniques. It has all the fields of use of conventional glass-filledPET plus additional ones provided by its superior physical propertiesand flame retardance. For example, in many electrical apparatus such asTV sets, glass-filled PET is too inflammable for the fabrication ofsmall parts such as brackets, chassis support components, or connectors.Our red phosphorous containing glass-filled PET is satisfactorily flameretardant and additionally, because of its superior physical properties,makes the apparatus more resistant to physical abuse such as droppingduring shipment or other handling.

It should also be noted, as heretofore indicated, that the beneficialphysical property and fire retardant effects of the combination of redphosphorous and metal oxide can also be imparted to non-glass-filledPET. The desired metal oxide and red phosphorous concentrations and particle size are the same as for glass-filled PET. In this case, oneachieves a fire retardant PET which can be extruded in filament form andthereafter transformed into various fibers and fabrics analogous toconventional unfilled PET. The only limitation is that the added redphosphorous and metal oxide affect the color of the unfilled PET so thatit cannot be used in applications where light or brightly colored PET isdesired. Where the phosphorous containing unfilled PET is moulded, themoulded article has physical properties superior to conventionalunfilled PET and is fire retardant as well. With glass-filled PET, thecolor of the material is ordinarily not significant, but if desired, thephosphorous containing glass-filled PET can be colored any desired darkshade by conventional coloring agents.

TEST METHODS Ultimate tensile strength, ultimate elongation, and initialmodulus are all determined in accordance with ASTM Test Method D638using a head speed of 0.1 inches/min.

Tensile strength is expressed in pounds per square inch, ultimateelongation in percent, initial modules in pounds per square inch/10 andIzod notch impact strength in ft. pounds/inch notch.

Izod notch impact strength was determined in accordance with ASTM TestMethod D256-61 at 23 C. and 50% relative humidity.

The Fenimore-Martin Oxygen Index Test employs a vertical glass tube 6.0cm. high and 8.4 cm. in diameter, in which a rod or strip specimen 8 cm.long is held vertically by a clamp at its bottom end. A mixture ofoxygen and nitrogen is metered into the bottom of the tube, passingthrough a bed or glass heads at the bottom to smooth the flow of gas.The sample is ignited at its upper end with a hydrogen flame which isthen withdrawn, and the atmosphere that permits steady burning down ofthe specimen is determined. The limiting oxygen index is the minimumfraction of oxygen in a nitrogen mixture which will just permit thesample to burn. Materials which have a limiting oxygen index greaterthan 0.21 are self-extinguishing after ignition in air if allowed toburn in the same manner as the test, i.e., from the top down.

The vertical Burn Test (Underwriter Laboratory Test Method No. 94) isused to judge whether or not a material of a given thickness can beclassified as self-extinguishing. It has subgroupings as follows: SE-Oif it extinguishes within 5 sec. (avg) and does not drip flamingparticles; SEI, if it extinguishes within 25 sec. (avg.) and does notdrip flaming particles; SE-II, if it extinguishes within 25 sec. (avg)but releases flaming particles or drips during that time. Materialswhich are not self-extinguishing are categorized as N.R. (non-rated).Ordinary glass-filled PET is N.R.

The SE-O flammability index is a new classification that was designed toidentify materials that can meet the more severe safety requirements ofcertain electrical apparatus that experience has shown can pose aspecific fire hazard; for example, enclosures of switches used for TVreceivers.

Test specimens are 6" in length by /2" in width by either A, /s", or Ain thickness. It is harder, of course, to obtain an SE-O rating withthick specimen than with thicker test specimens. The specimen is clampedvertically and a blue Bunsen burner flame applied to the bottom end ofthe specimen for a period of 10 seconds and then removed and theduration of flaming or glowing combustion of the specimen is noted. Ifflaming or glowing combustion of the specimen ceases within 30 secondsafter removal of the test flame, the test flame is again placed underthe specimen for 10 seconds immediately after flaming or glowingcombustion of the specimen stops. The test flame is again withdrawn, andthe duration of flaming or glowing combustion of the specimen againnoted.

If the specimen drips flaming particles or droplets while burning inthis test, these drippings are allowed to fall onto a horizontal layerof cotton fibers (untreated surgical cotton) placed 1 ft. below the testspecimen. Significant flaming particles are considered to be thosecapable of igniting the cotton fibers.

The duration of flaming or glowing combustion of vertical specimensafter application of the test flame, aver- 2. A composition inaccordance with claim 1 wherein said composition contains as anadditional component from about 5 to about 40 Weight percent glassfiber.

3. A composition in accordance with claim 1 wherein said phosphorous ispresent in an amount ranging from from about 2 to about 5 weightpercent.

4. A composition in accordance with claim 1 wherein said phosphorous hasa particle size of no greater than about 25 5. A composition inaccordance with claim 1 wherein said metal oxide is MgO, TiO ZnO, M orA1 0 6. A composition in accordance with claim 5 wherein said metaloxide is MgO.

7. A composition in accordance with claim 1 wherein said metal oxide isMgO, said red phosphorous is present in an amount ranging from about 2to about 5 weight percent, both said red phosphorous and said MgO have amaximum particle size of 25a and wherein said composition contains as anadditional component about 5 to about 40 weight percent glass fiber.

8. A process for enhancing the fire retardance of polyethyleneterephthalate comprising adding to said polyethylene terephthalate from0.5 to 10.0 weight percent finely particulate red phosphorous.

9. A composition comprising:

(a) polyethylene terephthalate and (b) from 0.5 to weight percent offinely particulate red phosphorous.

10. A composition as claimed in claim 9 additionally including fromabout 5 to about weight percent glass fiber.

11. A composition as claimed in claim 9 wherein said phosphorous ispresent in an amount ranging from about 2 to about 5 weight percent.

12. A composition as claimed in claim 9 wherein said red phosphorous hasa particle size of no greater than about 25 1..

References Cited S. M. PERSON, Assistant Examiner US. Cl. X.R.

26045.7 P, DIG. 24

-' MD STATES PATENT oFFIcE Po-wso (569 QERTIFFfiATE @F CGECTFN PatentNo. 3,8 7,86l Dated November l2, 197 4 Inventoflg) Theodore Largman andHerman Stone It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In the following lines change "phosphorous" to --phosphorus--.

Column 1, lines 13, 17, 56, 62, 63, 70

" Column 2, lines 4,, 9, 1o, 11, 15 17 22, 25, 28, 31,

l 35-36, 10, n3, a6,- 50-, 53, 6,6 4 Column 3,. lines 1, 6, 7 2 1, 29,3o, 19, 59-6o, 66, 68, 73 Column 1, lines 1, 6

Column 5, lines 21, 27, 41, 7 4

Column 6, lines 20, 38, 5 4 Column 7, lines 5 8, 15, 17, 2 4, 28

Column 8, lines 5 and 8 Signed and sealed this 18th day of February1975.

(SEAL) Y Attest 3 C. MARSHALL DANN RUTH (3 MASON Commissioner of PatentsAttestin'g Qffz'uzzer: and Trademarks

1. A COMPOSITION COMPRISING: (A) POLYETHYLENE TEREPHTHALATE (B) FROM 0.5TO 10 WEIGHT PERCENT OF FINELY PARTICULATE RED PHOSPHORUS (C) FROM 2.0TO 5.0 WEIGHT PERCENT OF A METAL OXIDE SELECTED FROM THE GROUPCONSISTING OF MGO, TIO2, ZNO, MOO3, AL2O3, ZR2O3, CR2O3, WO2O3, B2O3,MNO2, CDO, SNO, PB2O3, BI2O3, SB2O5.